Field
The present disclosure relates generally to helical piles, and more particularly to leads and extensions for helical piles having perimeter shear helical plates.
Description of the Related Art
Piles are used to support structures, such as buildings, when the soil underlying the structure would be too weak alone to support the structure. To effectively support a structure, a pile has to penetrate the soil to a depth where competent load-bearing stratum is found. Conventional piles can be cast in place by excavating a hole in the place where the pile is needed, or a hollow form can be driven into the ground where the pile is needed, and then filled with cement. These approaches are cumbersome and expensive.
Helical or screw piles are a cost-effective alternative to conventional cement piles because of the speed and ease at which a helical pile can be installed. Helical piles are rotated such that load bearing helical plates at the lower end of the pile effectively screw the pile into the soil to a desired depth. Referring to FIG. 1, a helical pile 10 is typically made of galvanized straight steel square or round shafts sequentially joined together. The bottom most piece of a helical pile is known as the lead 12, which has a lead head portion 14 and a lead end portion 16. The lead end portion 16 is configured to first penetrate the soil, and terminates at a pointed tip 17. As seen in FIGS. 1 and 2, the lead end portion 16 typically has one or more spaced apart load bearing helical plates 18 arranged on the lead shaft typically in the lead end portion 16 to penetrate the soil. The load bearing helical plates 18 on the lead may have the same diameter, or the load bearing helical plates may have different diameters that are in a tapered arrangement. For example, the tapered arrangement may be such that the smallest diameter load bearing helical plate is closest to the lead tip 17 and the largest load bearing helical plate is at a distance away from the lead tip. The load bearing helical plates 18 on the lead 12 are spaced apart at a distance “A” sufficient to promote individual plate load bearing capacity. Typically, the distance “A” is three times the diameter of the smallest load bearing helical plate 18 on the shaft of the lead 12. The diameter of the load bearing helical plates 18 in conventional helical piles may range from between about 6 inches and about 16 inches depending upon the load the pile is to carry. As noted above, helical piles 10 are installed by applying torque to the shaft at the lead head 14 that causes the load bearing helical plates to rotate and screw into the soil with minimal disruption to the surrounding soil. As the lead 12 penetrates the soil, one or more extensions 20 may have to be added to the pile 10 so that the pile can achieve the desired depth and load capacity. Referring to FIG. 1, extensions 20 may be fabricated from traditional straight steel square or round shafts and have an extension end portion 22 and an extension head portion 24 that are configured to connect to a lead head portion 14 and/or another extension 20, typically with a nut and bolt. Referring to FIG. 3, the extensions 20 may have load bearing helical plates 26 spaced apart at a distance “A” sufficient to promote individual plate load bearing capacity. As noted above, typically, the distance “A” is three times the diameter of the smallest load bearing helical plate 26 on the shaft of the extension 12. The diameter of the load bearing helical plates 26 in conventional helical pile extensions may range from between about 12 inches and about 16 inches depending upon the load the pile is to carry. Typically, the load bearing plates 26 on extension 20 are the same diameter as the largest load bearing helical plate on the lead 12.
One drawback of conventional helical piles is that they have a limited load capacity that if exceeded can cause the helical pile to settle or creep. Another drawback of conventional helical piles is that they can succumb to lateral movement. Greater pile stability and stiffness can be achieved by pouring or pumping cement based grout around the pile shaft which hardens to form a grout column. However, adding grout columns increase construction costs from a time and materials point of view. Further, there may be instances where soil conditions or other environmental conditions do not permit the use of grout columns to increase the stability, stiffness, and load capacity of the pile. The present disclosure provides an alternative to using grout columns to increase the stability, stiffness and load capacity of helical piles.